The present invention is directed to a telescoping boom crane having a multi-sectioned, telescopically extending boom.
Extremely heavy lifts and/or long-reach lifts have previously required the transportation in pieces, assembly and erection of pendant supported latticed boom cranes. The telescoping boom crane is normally more readily transportable, will erect with less time, labor and equipment and in a more confined space.
The present invention is especially useful as a boom for a mobile crane. Mobile cranes are lifting machines, capable of being moved around or between work sites. Manufacturers and users of the mobile crane must typically balance certain criteria such as total machine weight, cost, mobility, boom length and the net load lifting capacity of the machine, when selecting a crane. As an example, as a boom is made longer or stronger, it normally must be made heavier. The heavier boom requires a heavier, more expensive, less mobile structure to support it. Significant advantage can be achieved by use of a strong but light boom, capable of achieving longer telescoping ranges while maintaining rigidity of the boom under load.
As it turns out, the currently available crane capable of best balancing these criteria are boom cranes commonly referred to as the lattice boom cranes. These cranes feature pendant supported booms, which are hauled to the jobsite in sections and pinned together to achieve the desired boom length.
Lattice boom cranes are the best modern technology has been able to achieve for extremely heavy, extremely long-reach and long term, fast-paced production lifting. Unfortunately, the lattice boom cranes continue to suffer some serious drawbacks:
a) It is time consuming and expensive to move a lattice boom crane or change the boom length. Typically another crane, a crew of men, and a number of trucks to haul boom sections are required.
b) A large amount of clear ground and overhead area is required for assembly and disassembly of the crane sections. Many industrial plants and city construction sites simply do not have sufficient clear area necessary to assemble and tilt the boom up into a working position.
c) Assembly and disassembly of the crane has proven to be one of the most dangerous phases of crane operations. Many deaths and injuries occur each year by simple errors made in the manual pinning and/or unpinning procedure used for attaching boom sections and pendants together.
d) Typical supporting wire rope pendants have a relatively short safe life span. The wire rope pendants are cumbersome to handle. They are connected by dozens of pins with keepers, each critical. Frequent inspections for deterioration and correct assembly are required to be made by highly trained and diligent personnel.
e) The boom is very expensive to manufacture. Each section is made of dozens of cut and welded parts, which must be fitted exactly to insure true and straight sections.
Some problems with lattice boom cranes have been somewhat alleviated with the introduction of the telescoping boom cranes which began to appear more prevalently in the 1950""s. As the name implies, the telescoping cranes are fit with a boom made of multiple sections which nest one within the other. During transport between work sites, these cranes typically travel with the boom in a stowed or retracted position. Upon arrival on site, the boom may be quickly raised, then extended, ready to lift the load.
Unfortunately, this increased mobility comes with heretofore unsolvable drawbacks. One specific problem keeping the telescoping boom crane from making long and/or heavy lifts is the greater relative mass of the telescoping crane boom. Advances in mass reduction while retaining or increasing the strength and/or length of the telescopic crane boom have slowly decreased to incremental improvement over the last few decades. As compared to lattice booms, the telescoping booms have traditionally been subjected to significant bending stress from both the ram used to raise and lower the boom, as well as the load extending from the end of the boom. The lattice booms, on the other hand, are supported by a pendant system. Typically, the pendants are fastened to the upper end of the boom and to a mast well above the base of the boom and then the pendants are pulled upon in order to raise the boom. Axial compression forces are thereby placed on the boom, but very little bending occurs. Further, under load, the pendant system additionally provides support to that offered by the lattice structure itself. Simply substituting the lattice boom pendant system onto a telescopic crane would have its own complications in that it would require, among other considerations, a crew to erect and dismantle the system, transportation of the system and adequate space within which to erect and extend the boom.
The problems associated with currently available telescoping boom cranes are summarized as follows:
a) The boom is comparatively heavy, thereby causing a corresponding increase in the weight of the support structure needed to support it. Overall, the mobile crane is heavier, but can only lift lighter loads, especially as the load is moved further from the machine, (e.g. through extension of the boom).
b) The boom is very flexible, especially as the length increases. Flexibility causes problems with load positioning and control, and further expands cycle times on production jobs. Further, the difficulty associated with controlling a load hanging from a long, flexible boom tip causes increased operator stress and fatigue.
c) The booms are too short for many jobs.
d) The cranes lose capacity rapidly as the load radius (distance from machine) increases.
e) The cranes lose capacity rapidly as the boom length is increased.
f) The booms are expensive to build, typically requiring two or more full-length welds on rather heavy gauge material and considerable weldments and machining on both ends and at various intermediate positions for reinforcing, pin locking and adjustable slides.
Attempts to furnish pendant support for telescoping booms have been made. The SUPERLIFT by Demag Mobile Cranes, GmbH, is a system whereby wire rope is reeved through a mast and the boom tip. It typically features a large winch on the side of the boom, which tends to block the operator""s view, adds weight, and requires additional hydraulic circuitry. The pendant support provided on the SUPERLIFT is wire rope, which has a poor safe working-load-to-weight-ratio, a short life-span and requires frequent inspection by a skilled person. The SUPERLIFT has many sheaves or rollers which must be kept lubricated and inspected. Most importantly, the pendant support of the SUPERLIFT has not served to significantly lighten or lengthen the telescoping boom it supports, but is normally used as an add-on and erected only for extra-heavy lifts.
The present invention avoids these and other difficulties by providing an extending boom capable of lifting heavy loads.
The present invention is directed to a telescoping boom crane having a multi-sectioned, telescopically extending boom and an extensible pendant support system. The extending boom includes boom sections that are extensibly receivable within the adjacent boom section. The extensible pendant support system includes a plurality of pendants that are extensibly receivable within an adjacent pendant. The pendant support system at least partially supports the boom when a load is applied to the boom.
More particularly, the extending boom includes at least two boom sections: a tip boom section and a base boom section. Additionally, at least one intermediate boom section may be situated between the tip and base boom sections. The boom sections have successively smaller cross-sections and are extensibly receivable within the adjacent boom section. Each of the boom sections is made of a sheet material, which may or may not have corrugations, perforations or both, extending along a length of the sheet material. Further, the boom sections are columnar in shape. Lastly, a releasable locking mechanism may be attached to the boom sections to secure each of the boom sections and maintain positional relationship of the boom sections when the sections are in a fully extended position.
The extensible pendant support system includes a plurality of pendants including at least a tip pendant and a base pendant. Additionally, at least one intermediate pendant may be situated between the tip and base pendants. Each of the pendants is extensibly receivable within an adjacent pendant, and extension of the extending boom causes extension of the extensible pendant support system such that the extensible pendant support system at least partially supports the extending boom when a load is applied to the boom. The plurality of pendants may additionally form a forestay, which may be utilized with a mast and a backstay to form the extensible pendant support system. Further, the support system may include a forestay length locking device functioning to prohibit extension of a subsequent pendant from an adjacent pendant once the former pendant achieves an extended position.
It is further contemplated herein that the multi-sectioned, telescopically extending boom and the extensible pendant support system according to one embodiment of the present invention may be utilized in a partially extended configuration. Further a mechanism for telescopically advancing the boom sections may be provided.